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United States Patent |
6,134,058
|
Mohri
,   et al.
|
October 17, 2000
|
Object lens driving device
Abstract
An object lens driving device of the present invention includes a movable
section, supporting sections for supporting the movable section and a base
for holding the supporting sections. The movable section includes an
object lens for recording and/or reproducing optical information to and/or
from a disk-shaped recording medium, a lens holder for holding the object
lens and at least four permanent magnets adhered to the lens holder. The
supporting sections include at least four metal wires substantially
parallel to each other, each wire having a first end fixed to the lens
holder and a second end connected to the base, and elastic deformable
elements connected to the base and having connecting sections thereof
connected to the second end of each respective metal wire. The base
includes yokes fixed to the base and facing the respective permanent
magnets, focusing coils wound around the respective yokes, wound axes of
the focusing coils being oriented in a direction of an optical axis of the
object lens, and tracking coils wound around the respective yokes, wound
axes of the tracking coils being oriented in a direction perpendicular to
the wound axes of the focusing coils.
Inventors:
|
Mohri; Masanari (Hyogo, JP);
Fujii; Hitoshi (Osaka, JP);
Wakabayashi; Kanji (Kyoto, JP);
Yamamoto; Hiroshi (Kyoto, JP);
Takizawa; Teruyuki (Osaka, JP);
Santo; Takeo (Osaka, JP)
|
Assignee:
|
Matsushita Electric Industrial Co., Ltd. (Osaka, JP)
|
Appl. No.:
|
342585 |
Filed:
|
June 29, 1999 |
Foreign Application Priority Data
| Jul 03, 1998[JP] | 10-188650 |
| Oct 20, 1998[JP] | 10-298051 |
Current U.S. Class: |
359/824; 359/813; 359/814; 369/44.15 |
Intern'l Class: |
G02B 007/02; G11B 007/00 |
Field of Search: |
359/811,813,814,819,823,824
369/44.15,44.16
|
References Cited
U.S. Patent Documents
4773055 | Sep., 1988 | Gijzen et al. | 369/44.
|
5446721 | Aug., 1995 | Sekimoto et al. | 369/247.
|
5905255 | May., 1999 | Wakabayashi et al. | 250/201.
|
6016292 | Jan., 2000 | Lee | 369/44.
|
Foreign Patent Documents |
58-88841 | May., 1983 | JP.
| |
60-142822 | Sep., 1985 | JP.
| |
61-187134 | Aug., 1986 | JP.
| |
62-33345 | Feb., 1987 | JP.
| |
62-33346 | Feb., 1987 | JP.
| |
62-119742 | Jun., 1987 | JP.
| |
64-82341 | Mar., 1989 | JP.
| |
2-23536 | Jan., 1990 | JP.
| |
4-103042 | Apr., 1992 | JP.
| |
4-366429 | Dec., 1992 | JP.
| |
5-10249 | Mar., 1993 | JP.
| |
5-16647 | May., 1993 | JP.
| |
6-68844 | Aug., 1994 | JP.
| |
9-22537 | Jan., 1997 | JP.
| |
Primary Examiner: Epps; Georgia
Assistant Examiner: Seyrafi; Saud
Attorney, Agent or Firm: Ratner & Prestia
Claims
What is claimed is:
1. An object lens driving device, comprising:
a movable section;
supporting sections for supporting the movable section; and
a base for holding the supporting sections,
the movable section comprising:
an object lens for recording and/or reproducing optical information to
and/or from a disk-shaped recording medium:
a lens holder for holding the object lens; and
at least four permanent magnets adhered to the lens holder,
the supporting sections comprising:
at least four metal wires substantially parallel to each other, each wire
having a first end fixed to the lens holder and a second end connected to
the base; and
elastic deformable elements connected to the base and having connecting
sections thereof connected to the second end of each respective metal
wire, and
the base comprising:
yokes fixed to the base and facing the respective permanent magnets;
focusing coils wound around the respective yokes, wound axes of the
focusing coils being oriented in a direction of an optical axis of the
object lens; and
tracking coils wound around the respective yokes, wound axes of the
tracking coils being oriented in a direction perpendicular to the wound
axes of the focusing coils.
2. An object lens driving device according to claim 1, further comprising a
control section for applying electric currents to the respective focusing
coils, wherein
the control section switches directions of the electric currents to drive
the lens holder in a focusing direction, a radial tilt direction and a
tangential tilt direction.
3. An object lens driving device according to claim 1, wherein
the elastic deformable elements are board-shaped or rod-shaped; and
the connecting sections are elastic-deformable so that the second end of
each respective metal wire can displace along an axial direction of the
metal wire.
4. An object lens driving device according to claim 1, wherein
the yokes are provided to face the respective permanent magnets along the
axial direction of the metal wire;
the yokes and the permanent magnets are provided so that forces of tension
act on the metal wires; and
the forces of tension are generated by the addition of magnetic forces of
attraction between the yokes and the permanent magnets.
5. An object lens driving device according to claim 4, wherein distances
between the yokes and the permanent magnets are provided so that forces of
tension act on the metal wires.
6. An object lens driving device according to claim 4, wherein thicknesses
of the yokes along the axial direction of the metal wire are provided so
that forces of tension act on the metal wires.
7. An object lens driving device according to claim 4, wherein spring
forces necessary for the connecting sections to deform along axial
directions of the respective metal wires are greater than at least the
respective magnetic forces of attraction.
8. An object lens driving device according to claim 1, wherein the lens
holder comprises:
relaying elements, the first end of the metal wire being connected to each
relaying element;
a main body of the lens holder for holding the object lens; and
elastic deformable elements for interconnecting the main body of the lens
holder and the relaying elements, deforming so that the main body of the
lens holder pivots in a tangential tilt direction.
9. An object lens driving device, comprising:
a movable section;
supporting sections for supporting the movable section; and
a base for holding the supporting sections,
the movable section comprising:
an object lens for recording and/or reproducing optical information to
and/or from a disk-shaped recording medium;
a lens holder for holding the object lens; and
at least two permanent magnets adhered to the lens holder,
the supporting sections comprising:
at least four metal wires substantially parallel to each other, each wire
having a first end fixed to the lens holder and a second end connected to
the base,
the base comprising:
yokes fixed to the base and facing the respective permanent magnets;
focusing coils wound around the respective yokes, wound axes of the
focusing coils being oriented in a direction of an optical axis of the
object lens; and
tracking coils wound around the respective yokes, wound axes of the
tracking coils being oriented in a direction perpendicular to the wound
axes of the focusing coils, and
the lens holder comprising:
relaying elements, the first end of the metal wire being connected to each
relaying element;
a main body of the lens holder for holding the object lens; and
elastic deformable elements for interconnecting the main body of the lens
holder and the relaying elements, deforming so that the main body of the
lens holder pivots in a tangential tilt direction.
10. An object lens driving device according to claim 9, wherein the elastic
deformable element comprises a flat spring that has a pivotal axis and
deforms by twisting around the pivotal axis so that the main body of the
lens holder pivots in a tangential tilt direction, the flat spring having
L-shaped or +-shaped cross-section thereof.
11. An object lens driving device according to claim 9, wherein the elastic
deformable element is hinge-shaped.
12. An object lens driving device according to claim 9, wherein the elastic
deformable element has a pivotal axis and deforms by twisting around the
pivotal axis so that the main body of the lens holder pivots in a
tangential tilt direction, and
the elastic deformable element is provided so that the pivotal axis passes
through a center of mass of the movable section.
13. An object lens driving device according to claim 9, wherein the elastic
deformable element has a pivotal axis and deforms by twisting around a
pivotal axis so that the main body of the lens holder pivots in a
tangential tilt direction, and
the elastic deformable element is provided so that the pivotal axis passes
through a principal point of the object lens.
14. An object lens driving device according to claim 9, wherein the elastic
deformable element comprises a flat spring that has a pivotal axis and
deforms by twisting around the pivotal axis so that the main body of the
lens holder pivots in a tangential tilt direction, and the flat spring is
covered with a damping material.
15. An object lens driving device according to claim 9, wherein a returning
force generated by a pivotal movement of the elastic deformable element is
greater than at least a magnetic force of attraction around the pivotal
axis generated between the yoke and the permanent magnet.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an object lens driving device used in an
optical information recording and/or reproduction apparatus for recording
information to and/or reproducing information from a disk-shaped recording
medium.
2. Description of the Related Art
If a disk-shaped recording medium (hereinafter, simply referred to as
"disk") is warped, the distance between the surface of the recording
medium and an object lens of the object lens driving device varies as the
recording medium rotates, resulting in a focusing error. If the rotation
of the recording medium is off-center, a tracking error occurs. In order
to prevent a focusing or tracking error, an object lens driving device
controls the object lens to be driven in two directions, namely, along the
optical axis of the object lens which is vertical to the surface of the
recording medium (focusing direction) and along the direction parallel to
the surface of the recording medium (tracking direction).
In the optical information recording and/or reproduction apparatus
incorporating the object lens driving device as described above, a
relative tilt of the optical axis of the object lens to the surface of a
disk (hereinafter, simply referred to as "tilt") may occur besides the
focusing error and the tracking error. The tilt is responsible for optical
aberration which deteriorates signals during recording and reproduction.
Some conventional optical information recording and/or reproduction
apparatus have been proposed for solving the above problems. For example,
Japanese Laid-Open Publication No. 9-22537 discloses that the tilt is
corrected by providing at least one permanent magnet adhered to a movable
section and at least two focusing coils attached on a base and regulating
currents flowing through the coils.
Such a conventional optical information recording and/or reproduction
apparatus will be described below with reference to the accompanying
drawings. FIG. 11 is a perspective view of a structure of the conventional
optical information recording and/or reproduction apparatus 500. FIG. 12
is a diagram for explaining the definitions of the reference symbols of
the present specification.
Referring to FIG. 11, the apparatus 500 includes an object lens 101, a lens
holder 102 for holding the object lens 101, permanent magnets 103a and
103b adhered to the lens holder 102, suspension wires 104, opposed yokes
105a-105d, tracking coils 106a-106d, focusing coils 107a-107d, a
suspension holder 108, and a fixation base 109. The object lens 101, the
lens holder 102, and the permanent magnets 103a and 103b constitute a
movable section 550. A first end of each suspension wire 104 is attached
to the movable section 550 while one end of each suspension wire 104 is
attached to the suspension holder 108.
Referring to FIG. 12, moving directions of the movable section 550 are
defined. In FIG. 12, Fo indicates a focusing direction parallel to an
optical axis; Tr a tracking direction perpendicular to the direction Fo;
Rt a radial tilt which is a tilt around the axis of a tangential
direction; and Tt a tangential tilt which is a tilt around the axis of the
tracking direction.
Now the operation of the conventional object lens driving apparatus 500
will be described with reference to FIG. 11. The movable section 550 is
driven toward the tracking direction Tr by electromagnetic forces
generated by electric currents through the tracking coils 106a-106d
traversing in a direction perpendicular to the magnetic flux of the
permanent magnets 103a and 103b. Since the tracking coils 106a-106d are
fixed on the base 109, the movable section 550 performs its relative
substantially translational movement.
The movable section 550 is also driven toward the focusing direction Fo by
electromagnetic forces generated by electric currents through the focusing
coils 107a-107d traversing in a direction perpendicular to the magnetic
flux of the permanent magnets 103a and 103b, performing its substantially
translational movement.
Furthermore, the movable section 550 is driven along the direction of the
radial tilt Rt by the moment Mr of a force around the Y axis produced by
applying to the movable section 550 a driving force in the direction Fo by
the focusing coils 107a and 107c and a driving force in the direction Fo,
but in the opposite direction, by the focusing coils 107b and 107d.
According to this, it is possible to correct the radial tilt.
To enhance the recording capacity of an optical information recording
and/or reproduction apparatus using disks, a condensed light spot used for
recording and reproducing information to and from the disk has been
increasingly made narrower by adopting an object lens having a higher
aperture ratio. In this case, the optical aberration caused by the
relative tilt of the optical axis of the object lens to the surface of the
disk increases in proportion to the third power of the aperture ratio. To
obtain satisfactory recording and reproduction signals, it is therefore
required to correct the tilt of the optical axis of the object lens to the
disk.
Although the above-described structure makes it possible to correct a tilt
in a radial direction caused by the warp of a disk and the like, so-called
radial tilt, it is difficult to correct a tilt in a tangential direction
caused by the bend of a disk, so-called tangential tilt.
The present invention is provided to solve the above problems with the
conventional object lens driving device.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an object lens driving
device includes a movable section, supporting sections for supporting the
movable section and a base for holding the supporting sections. The
movable section includes an object lens for recording and/or reproducing
optical information to and/or from a disk-shaped recording medium, a lens
holder for holding the object lens and at least four permanent magnets
adhered to the lens holder. The supporting sections include at least four
metal wires substantially parallel to each other, each wire having a first
end fixed to the lens holder and a second end connected to the base, and
elastic deformable elements connected to the base and having connecting
sections thereof connected to the second end of each respective metal
wire. The base includes yokes fixed to the base and facing the respective
permanent magnets, focusing coils wound around the respective yokes, wound
axes of the focusing coils being oriented in a direction of an optical
axis of the object lens, and tracking coils wound around the respective
yokes, wound axes of the tracking coils being oriented in a direction
perpendicular to the wound axes of the focusing coils.
In one embodiment of the present invention, the object lens driving further
includes a control section for applying electric currents to the
respective focusing coils, in which the control section switches
directions of the electric currents to drive the lens holder in a focusing
direction, a radial tilt direction and a tangential tilt direction.
In another embodiment of the present invention, the elastic deformable
elements are board-shaped or rod-shaped and the connecting sections are
elastic-deformable so that the second end of each respective metal wire
can displace along an axial direction of the metal wire.
In still another embodiment of the present invention, the yokes are
provided to face the respective permanent magnets along the axial
direction of the metal wire. The yokes and the permanent magnets are
provided so that forces of tension act on the metal wires. The forces of
tension are generated by the addition of magnetic forces of attraction
between the yokes and the permanent magnets.
In still another embodiment of the present invention, distances between the
yokes and the permanent magnets are provided so that forces of tension act
on the metal wires.
In still another embodiment of the present invention, thicknesses of the
yokes along the axial direction of the metal wire are provided so that
forces of tension act on the metal wires.
In still another embodiment of the present invention, spring forces
necessary for the connecting sections to deform along axial directions of
the respective metal wires are greater than at least the respective
magnetic forces of attraction.
In still another embodiment of the present invention, the lens holder
includes relaying elements, the first end of the metal wire being
connected to each relaying element, a main body of the lens holder for
holding the object lens and elastic deformable elements for
interconnecting the main body of the lens holder and the relaying
elements, deforming so that the main body of the lens holder pivots in a
tangential tilt direction.
According to another aspect of the present invention, an object lens
driving device includes a movable section, supporting sections for
supporting the movable section and a base for holding the supporting
sections. The movable section includes an object lens for recording and/or
reproducing optical information to and/or from a disk-shaped recording
medium, a lens holder for holding the object lens and at least two
permanent magnets adhered to the lens holder. The supporting sections
include at least four metal wires substantially parallel to each other,
each wire having a first end fixed to the lens holder and a second end
connected to the base. The base includes yokes fixed to the base and
facing the respective permanent magnets, focusing coils wound around the
respective yokes, wound axes of the focusing coils being oriented in a
direction of an optical axis of the object lens, and tracking coils wound
around the respective yokes, wound axes of the tracking coils being
oriented in a direction perpendicular to the wound axes of the focusing
coils. The lens holder includes relaying elements, the first end of the
metal wire being connected to each relaying element, a main body of the
lens holder for holding the object lens and elastic deformable elements
for interconnecting the main body of the lens holder and the relaying
elements, deforming so that the main body of the lens holder pivots in a
tangential tilt direction.
In one embodiment of the present invention, the elastic deformable element
includes a flat spring that has a pivotal axis and deforms by twisting
around the pivotal axis so that the main body of the lens holder pivots in
a tangential tilt direction, the flat spring having L-shaped or +-shaped
cross-section thereof.
In another embodiment of the present invention, the elastic deformable
element is hinge-shaped.
In still another embodiment of the present invention, the elastic
deformable element has a pivotal axis and deforms by twisting around the
pivotal axis so that the main body of the lens holder pivots in a
tangential tilt direction. The elastic deformable element is provided so
that the pivotal axis passes through a center of mass of the movable
section.
In still another embodiment of the present invention, the elastic
deformable element has a pivotal axis and deforms by twisting around a
pivotal axis so that the main body of the lens holder pivots in a
tangential tilt direction. The elastic deformable element is provided so
that the pivotal axis passes through a principal point of the object lens.
In still another embodiment of the present invention, the elastic
deformable element includes a flat spring that has a pivotal axis and
deforms by twisting around the pivotal axis so that the main body of the
lens holder pivots in a tangential tilt direction, and the flat spring is
covered with a damping material.
In still another embodiment of the present invention, a returning force
generated by a pivotal movement of the elastic deformable element is
greater than at least a magnetic force of attraction around the pivotal
axis generated between the yoke and the permanent magnet.
Thus, the invention described herein makes possible the advantages of (1)
providing an object lens driving device which can correct positions of a
movable section with respect to a disk in a tangential tilt direction, as
well as a focusing direction, a tracking direction and a radial tilt
direction; and (2) providing an object lens driving device which has
optimal drive characteristics by providing design freedom of a spring
constant defining sensitivity in a low-frequency region (first-order
resonant frequency region) for tangential tilt correction.
These and other advantages of the present invention will become apparent to
those skilled in the art upon reading and understanding the following
detailed description with reference to the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a perspective view illustrating a portion of a structure of an
object lens driving device according to Example 1 of the present
invention.
FIG. 1B is a perspective view illustrating another portion of a structure
of an object lens driving device according to Example 1 of the present
invention.
FIG. 2A is a schematic diagram illustrating a radial tilt movement in
Example 1 of the present invention.
FIG. 2B is a side view illustrating a radial tilt movement in Example 1 of
the present invention.
FIG. 2C is a side view illustrating a radial tilt movement in a direction
+Rt in Example 1 of the present invention.
FIG. 2D is a side view illustrating a radial tilt movement in a direction
-Rt in Example 1 of the present invention.
FIG. 3A is a schematic diagram illustrating a tangential tilt movement in
Example 1 of the present invention.
FIG. 3B is a side view illustrating a tangential tilt movement in Example 1
of the present invention.
FIG. 3C is a side view illustrating a tangential tilt movement in a
direction +Tt in Example 1 of the present invention.
FIG. 3D is a side view illustrating a tangential tilt movement in a
direction -Tt in Example 1 of the present invention.
FIG. 4A is a schematic diagram illustrating connections of focusing coils
and directions of electric currents for a drive in a focusing direction Fo
in Example 4 of the present invention.
FIG. 4B is a schematic diagram illustrating connections of focusing coils
and directions of electric currents for a drive in a radial direction Rt
in Example 4 of the present invention.
FIG. 4C is a schematic diagram illustrating connections of focusing coils
and directions of electric currents for a drive in a tangential direction
Tt in Example 4 of the present invention.
FIG. 5A is a schematic diagram illustrating directions of electric currents
for a drive in a focusing direction Fo in Example 4 of the present
invention.
FIG. 5B is a schematic diagram illustrating directions of electric currents
for a drive in a radial direction Rt in Example 4 of the present
invention.
FIG. 5C is a schematic diagram illustrating directions of electric currents
for a drive in a tangential direction Tt in Example 4 of the present
invention.
FIG. 6A is a schematic diagram illustrating a structure of an object lens
driving device according to Example 2 of the present invention.
FIG. 6B is a schematic diagram illustrating a structure of an object lens
driving device according to Example 3 of the present invention.
FIG. 7 is a perspective view illustrating a structure of an object lens
driving device according to Example 4 of the present invention.
FIG. 8 is an exploded perspective view illustrating a definition of drive
directions in Example 4 of the present invention.
FIG. 9 is an exemplary diagram illustrating rotation around a rotational
axis for a tangential drive according to Example 4 of the present
invention.
FIG. 10 is a schematic diagram illustrating an object lens driving device
employing hinges as elastic deformable elements according to Example 4 of
the present invention.
FIG. 11 is a perspective view illustrating a structure of an object lens
driving device in the prior art.
FIG. 12 is a diagram for explaining definitions of reference symbols in the
present specification.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Examples of the present invention will be described below with reference to
the accompanying drawings.
EXAMPLE 1
FIGS. 1A and 1B are perspective views of an object lens driving device 100
according to Example 1 of the present invention. FIGS. 2A-2D are schematic
diagrams illustrating radial tilt movements of a movable section. FIGS.
3A-3D are schematic diagrams illustrating tangential tilt movements of the
movable section.
Referring to FIGS. 1A and 1B, the device 100 includes an object lens 1, a
lens holder 2 for holding the object lens 1, permanent magnets 3a-3d
adhered to the lens holder 2, suspension wires 4, opposed yokes 5a-5d,
tracking coils 6a-6d, focusing coils 7a-7d, a suspension holder 8, a
fixation base 9, and a tilt spring 10. Reference symbols Ha-Hd indicate
directions of magnetization of the permanent magnets 3a-3d; Tr a tracking
direction; Fo a focusing direction; Rt a radial tilt direction: Tt a
tangential tilt direction; .+-.Fa-.+-.Fd directions of electric current
through the focusing coils 7a-7d, respectively; and .+-.Ta-.+-.Td
directions of electric currents through the tracking coils 6a-6d,
respectively. Note that the above directions of electric currents having
negative signs are not shown. The Tr to Tt directions have been previously
defined with reference to FIG. 12.
The object lens 1, the lens holder 2, and the permanent magnets 3a-3d
constitute a movable section 150. A first end of each suspension wire 4 is
attached to the movable section 150 while a second end of each suspension
wire 4 is attached to the tilt spring 10. The tilt spring 10 is further
fixed to the fixation base 9 via the suspension holder 8. The movable
section 150 is driven by electromagnetic forces generated by interaction
of magnetic fields of the permanent magnets 3a-3d adhered thereto and
electric currents past through the tracking coils 6a-6d and the focusing
coils 7a-7d made by winding wire around the yokes 5a-5d fixed to the
fixation base 9.
Next, the movement and driving of the movable section 150 will be described
with reference to FIGS. 1A and 1B. As shown in FIGS. 1A and 1B, the
movable section 150 is supported by the four suspension wires 4 so that it
can perform translational movements in the Fo and Tr directions. Each
direction is defined in FIG. 12.
The force of driving the movable section 150 toward the focusing direction
+Fo is generated by electric currents flowing through the focusing coils
7a-7d toward the directions +Fa, +Fb, +Fc and +Fd, respectively. Then, the
movable section 150 translationally moves toward the focusing direction
+Fo. The force of driving the movable section 150 toward the tracking
direction +Tr is generated by electric currents flowing through the
focusing coils 6a-6d toward the directions +Ta, +Tb, +Tc and +Td,
respectively. Then, the movable section 150 translationally moves toward
the direction +Tr.
Next, the driving and supporting of the movable section 150 in the radial
tilt direction Rt will be described with reference to FIGS. 2A-2D. FIG. 2A
is a partial perspective view illustrating the movable section 150, the
suspension wires 4 and the tilt spring 10. FIGS. 2B-2D are side views of
the movable section 150 as seen in the direction of an arrow VR of FIG.
2A.
In FIGS. 2A-2D, reference symbol Y indicates the Y axis defined in FIG. 12;
r indicates the distance between the Y axis and the center of the
suspension wire 4; .+-.Mr the moment of a force around the Y axis acting
on the movable section 150; 4' positions of the suspension wires 4 after
they have been driven toward the radial tilt direction Rt; and .+-.Foa-Fod
driving forces acting on the movable section 150.
In FIG. 2A, the driving forces -Foa, +Fob, -Foc and +Fod are produced by
electric currents flowing through the focusing coils 7a-7d of FIGS. 1A and
1B in the directions -Fa, +Fb, -Fc and +Fd, respectively. Movements of the
movable section 150 in the radial tilt direction when the driving forces
-Foa, +Fob, -Foc and +Fod act on the movable section 150 will be described
with reference to FIGS. 2B-2D. FIG. 2B illustrates a state (initial state)
of the movable section 150 when no driving force acts thereon. FIGS. 2C
and 2D illustrate states of the movable section 150 with radial tilts Rt.
As shown in FIG. 2C, the addition of the driving forces -Foa, +Fob, -Foc
and +Fod acts on the movable section 150 as the moment of the force +Mr
around the Y axis. The moment of the force +Mr makes each suspension wire
4 twisted in such a way that the end of the suspension wire 4 attached to
the movable section 150 follows along a circle with the radius r.
FIG. 2D illustrates the movable section 150 driven by the moment of the
force -Mr in a direction opposite to the moment of the force +Mr of FIG.
2C. The moment of the force -Mr is produced by electric currents flowing
through the focusing coils 7a-7d in the opposite directions to those in
the case of FIG. 2C.
As described above, the movable section 150 is supported by the deformable
suspension wires 4 so that the movable section 150 can be driven in the
radial direction Rt by controlling the directions of flow of electric
currents through the focusing coils 7a-7d.
Next, the driving and supporting of the movable direction 150 in the
tangential tilt direction Tt will be described with reference to FIGS.
3A-3D. FIG. 3A is a partial perspective view illustrating the movable
section 150, the suspension wires 4 and the tilt spring 10. FIGS. 3B-3D
are side views of the movable section 150 as seen in the direction of an
arrow Vt of FIG. 3A.
In FIGS. 3A-3D, reference numeral 10a indicates pivotal axes of the
deformable tilt spring 10; 4A fixation sections of the suspension wires 4
at which a second end of each suspension wire 4 is fixed to the tilt
spring 10; X the X axis defined in FIG. 6; .+-.Mt the moment of a force
around the X axis acting on the movable section 150; and .+-.Foa-.+-.Fod
driving forces acting on the movable section 150.
In FIG. 3A, the driving forces +Foa, +Fob, -Foc and -Fod are produced by
electric currents flowing through the focusing coils 7a-7d of FIGS. 1A and
1B in the directions +Fa, +Fb, -Fc and -Fd, respectively. Movements of the
movable section 150 in the tangential tilt direction when the driving
forces +Foa, +Fob, -Foc and -Fod act on the movable section 150 will be
described with reference to FIGS. 3B-3D.
FIG. 3B illustrates a state (initial state) of the movable section 150 when
no driving force acts thereon. FIGS. 3C and 3D illustrate states of the
movable section 150 with the tangential tilts Tt. As described in FIG. 3C,
the addition of the driving forces +Foa, +Fob, -Foc and -Fod acts on the
movable section 150 as the moment of the force +Mt around the X axis. The
moment of the force +Mt acts on each suspension wire 4 as a buckling force
of tension and compression. As shown in FIGS. 3C and 3D, the tilt spring
10 Is deformed around the pivotal axes 10a.
The fixation section 4A of the suspension wire 4 is displaced in the
tension or compression direction by the deformation of the tilt spring 10.
Thus, the movable section 150 can move along the tangential tilt direction
Tt in proportion to the amount of the displacement of the fixation section
4A.
As described above, according to Example 1, the driving means are deployed
at the four positions and the tilt spring 10 supports the fixation
sections 4A of the suspension wires 4 to be displaceable in the tension
and compression directions, whereby the movable section 150 can be driven
and supported in such a manner that the movable section 150 can readily
move in the focusing direction Fo, the tracking direction Tr, the radial
tilt direction Rt and the tangential tilt direction Tt.
It should be noted that the tilt spring 10 may be replaced with a rod-like
elastic supporting element and the bend or twist deformation of the
supporting element makes the fixation section 4A of the suspension wire 4
displaced in the tension and compression directions, thereby obtaining the
same functions and effects.
Moreover, the form of the fixation section 4A of the suspension wire 4 may
be changed so that the above rod-like elastic supporting element and the
suspension wires 4 are combined into an integral unit, thereby obtaining
the same functions and effects. Furthermore, when the rod-like elastic
supporting element and the suspension wires 4 are integrated, the tilt
spring 10 effectively becomes unnecessary.
FIGS. 4A-4C are schematic diagrams illustrating the directions of electric
currents through the focusing coils 7a-7d and the connections between the
focusing coils 7a-7d and a focusing coil driving circuit 11. Referring to
FIGS. 4A-4C, the focusing coil driving circuit 11 controls the directions
and amounts of electric currents through the focusing coils 7a-7d,
respectively.
FIG. 4A illustrates directions of electric currents through the focusing
coils 7a-7d for driving the movable section 150 toward the focusing
direction Fo. FIG. 4B illustrates directions of electric currents through
the focusing coils 7a-7d for driving the movable section 150 toward the
radial tilt direction Rt. FIG. 4C illustrates directions of electric
currents through the focusing coils 7a-7d for driving the movable section
150 toward the tangential tilt direction Tt.
The focusing coils 7a-7d and the focusing coil driving circuit 11 are
connected as shown in FIGS. 4A-4C. This connection is such that when the
movable section 150 is driven toward the focusing direction Fo, electric
currents flow through the focusing coils 7a-7d as if the focusing coils
7a-7d are connected as shown in FIG. 5A.
When the movable section 150 is driven toward the radial tilt direction Rt,
electric currents flow through the focusing coils 7a-7d as if the focusing
coils 7a-7d are connected as shown in FIG. 5B. The direction of electric
currents through the focusing coils 7a and 7c is opposite to that through
the focusing coils 7b and 7d.
When the movable section 150 is driven toward the tangential tilt direction
Tt, electric currents flow through the focusing coils 7a-7d as if the
focusing coils 7a-7d are connected as shown in FIG. 5C. The direction of
electric currents through the focusing coils 7a and 7b is opposite to that
through the focusing coils 7c and 7d.
It should be noted that the amounts of driving currents through the
focusing coils 7a-7d may be changed based on focusing error signals or
tracking error signals, thereby obtaining satisfactory control features.
EXAMPLE 2
FIG. 6A is a schematic diagram illustrating a structure of an object lens
driving device 200 according to Example 2 the present invention. In FIG.
6A, reference symbols Ga-Gd indicate gaps between permanent magnets 3a-3d
and opposed yokes 5a-5d, respectively; Da-Dd thicknesses of the opposed
yokes 5a-5d in the direction of a magnetic field; .+-.Mf a magnetic force
caused by magnetic forces of attraction between the permanent magnets
3a-3d and the opposed yokes 5a-5d, acting on a movable section 150; and Tw
a force of tension produced by the above-described magnetic attraction
force, acting on suspension wires 4.
Referring to FIG. 6A, the permanent magnets 3a-3d and the opposed yokes
5a-5d are provided in such a relative relationship that Ga<Gc and Gb<Gd.
The magnetic attraction force decreases in inverse proportion to the sizes
of the gaps Ga-Gd. Accordingly, a magnetic force acts on the movable
section 150 toward the direction +Mf, thereby providing a tension along
the direction Tw for each suspension wire 4.
As described above, according to Example 2, the deformation, such as
buckling, of the suspension wires 4 can be avoided, resulting in
consistently stable supporting of the movable section.
It should be noted that the thicknesses Da-Dd may be provided in such a
relationship that Da>Dc and Db>Dd, instead of setting the above
relationship of the gaps Ga-Gd. The magnetic attraction force increases in
proportion to the thickness of the yoke. Therefore, in such a setting, a
magnetic force acts on the movable section 150 toward the direction +Mf,
thereby providing a tension along the direction Tw for each suspension
wire 4. In this case, accordingly, the same functions and effects as
described above can be obtained.
EXAMPLE 3
FIG. 6B is a schematic diagram illustrating a structure of an object lens
driving apparatus 300 according to Example 3 of the present invention. In
FIG. 6B, reference symbols Ua-Ud indicate reaction forces (spring forces)
against the respective tensions Tw of the suspension wires 4 acting on
each bending section of the a tilt spring 10.
According to Example 3, the spring forces Ua-Ud of the tilt spring 10 are
provided so that Ua>Tw, Ub>Tw, Uc>Tw and Ud>Tw. Each of the spring forces
Ua-Ud of the tilt spring 10 is set to be less than a spring force in a
buckling direction of the suspension wire 4.
As described above, according to Example 3, with the tension Tw provided
for stably supporting a movable section as described in Example 2,
precision of positioning the movable section can be maintained while the
influence of buckling resonance of suspension wires upon the movable
section can be reduced.
EXAMPLE 4
FIG. 7 is a perspective view illustrating an object lens driving device 400
according to Example 4 of the present invention. FIG. 8 is a perspective
view, partially exploded, of the object lens driving device 400 for
defining driving directions thereof. FIGS. 9A and 9B are exemplary
diagrams illustrating pivotal movements of a movable section around a
pivotal axis by a tangential drive. The present invention relates to an
arrangement for the tangential drive which will be described in Example 4
by presenting an example of an object lens driving device performing a
3-axis drive including a tangential drive, a focusing drive and a tracking
drive. The present invention is not limited to this. The present invention
can be applied to an object lens driving device performing a 4-axis drive
as described in Example 1.
Referring to FIGS. 7 and 8, the device 400 includes an object lens 1, a
lens holder 2, permanent magnets 3a and 3b, suspension wires 4a-4d,
opposed yokes 5a and 5b, tracking coils 6a and 6b, focusing coils 7a and
7b, a suspension holder 8, a fixation base 9, elastic deformable elements
10a and 10b, and relaying elements 11a and 11b. Reference numeral 12
indicates a disk. Reference symbol O indicates the center of mass of a
movable section 450.
Driving directions of the movable section 450 will be defined with
reference to FIG. 8. As is defined in FIG. 12, reference symbols .+-.Fo
indicate focusing directions perpendicular to the recording surface of a
disk toward which the movable section 450 moves in focusing; .+-.Tr
tracking directions that are radial directions toward which the movable
section 450 moves in tracking; and .+-.Tt tangential tilt directions along
a circle of the disk recording surface toward which the movable section
tilts.
The object lens 1, the lens holder 2, the permanent magnets 3a and 3b, the
elastic deformable elements 10a and 10b, and the relaying elements 11a and
11b constitute the movable section 450, where the permanent magnets 3a and
3b are adhered to the lens holder 2, the relaying elements 11a and 11b are
connected to the lens holder 2 via the elastic deformable elements 10a and
10b. The suspension wires 4a-4d each have a first end thereof attached to
the suspension holder 8 provided on the fixation base 9 and a second end
thereof attached to the relaying elements 11a and 11b, supporting the
movable section 450 in such a manner that the displacement of the movable
section 450 is adjustable both in the focusing direction and in the
tracking direction. The tracking coils 6a and 6b and the focusing coils 7a
and 7b are provided around the opposed yokes 5a and 5b, respectively. The
opposed yokes 5a and 5b are positioned in a manner to face the permanent
magnets 3a and 3b, respectively, and fixed to the fixation base 9.
The elastic deformable elements 10a and 10b interconnect the lens holder 2
and the relaying elements 11a and 11b to which the suspension wires 4a-4d
are attached. According to this arrangement, the lens holder 2 is
supported in such a manner that the lens holder 2 can pivot around the
axes of the elastic deformable elements 10a and 10b, i.e., in the
tangential tilt direction .+-.Tt. Extensions of the pivotal axes of the
elastic deformable elements 10a and 10b both pass through the center of
mass O of the movable section 450 as shown in FIG. 8.
Next, the driving and controlling of the movable section 450 will be
described. The focusing drive is performed by exerting on the permanent
magnets 3a and 3b electromagnetic forces generated by the permanent
magnets 3a and 3b being influenced by the electromagnetic flux of the
focusing coils 7a and 7b through which electric currents flow so that the
electromagnetic forces are directed toward the same direction +Fo. In a
similar manner, the tracking drive is performed by exerting on the
permanent magnets 3a and 3b electromagnetic forces generated by the
permanent magnets 3a and 3b being influenced by the electromagnetic flux
of the focusing coils 6a and 6b through which electric currents flow so
that the electromagnetic forces are directed toward the same direction
+Tr. In focusing and tracking of a disk, errors may occur due to
fluctuations of the disk such as wobbling and off-center rotation. To
correct such errors, an error detecting means (not shown) is provided for
detecting the shift of a light beam caused by the fluctuations of the disk
and outputting error signals. The focusing and tracking are performed so
that the error signal is consistently minimized by servo control using
such error signals.
The tangential drive is performed by exerting on the permanent magnets 3a
and 3b electromagnetic forces in opposite directions +Fo and -Fo (or -Fo
and +Fo), respectively, generated by controlling directions of electric
currents through the focusing coils 7a and 7b. The electromagnetic forces
in the opposite directions generate the moment of rotation along the
direction .+-.Tt, which forces the movable section 450 to move along the
tangential tilt direction. In this case, the pivotal axis is each axis of
the elastic deformable elements 10a and 10b. Tangential tilt control is
performed by the tangential drive, referring to an error signal from a
tilt detecting means (not shown) such as a tilt sensor, so that a tilt is
consistently minimized or a time-based error signal (jitters) is
consistently optimized. Thus, optical aberration of the object lens 1
caused by the tilt is removed, thereby realizing stable recording and
reproduction.
Next, the elastic deformable elements 10a and 10b will be described in
detail. The effects thereof will be also described. The elastic deformable
elements 10a and 10b are flat springs made of a spring material such as
phosphor bronze which are deformable to be twisted. The cross-sections
perpendicular to the axis, of the elements 10a and 10b, are L-shaped or
+-shaped. The elastic deformable elements 10a and 10b shown in FIG. 7 have
+-shaped sections. The elements 10a and 10b are sufficiently flexible in a
pivotal direction around the axes thereof while being very rigid in a
direction perpendicular to the axes thereof. Therefore, the movable
section 450 can pivot around the axes of the elements 10a and 10b, but
cannot translationally move in a direction perpendicular to the axes.
Thus, unnecessary displacement of the movable section 450 is suppressed,
thereby realizing stable movements thereof.
The spring constant along the pivotal direction, of the elastic deformable
elements 10a and 10b, can be arbitrarily adjusted by changing the axial
length, thickness and shape thereof. By providing an appropriate setting,
optimal drive sensitivity can be obtained in a low frequency region of
tangential tilt-drive characteristics.
The suspension wires 4a-4d are each attached at a first end thereof to the
rigid relaying elements 11a and 11b and at a second end thereof to the
rigid suspension holder 8 in such a manner that the suspension wires 4a
and 4b and the suspension wires 4c and 4d are, in each pair, parallel to
each other and arranged side by side along the focusing direction.
Therefore, even when the movable section 450 moves in the focusing
direction and the suspension wires 4a-4d bend, the movable section 450
moves while keeping virtual planes, which are defined by the suspension
wires 4a and 4b and the suspension wires 4c and 4d respectively, both
substantially parallel to the focusing direction. Therefore, the movable
section 450 is driven while maintaining a substantially constant attitude
thereof.
It should be noted that the twist flat spring constant is determined so
that returning forces around the pivotal axes of the elastic deformable
elements 10a and 10b are greater than magnetic attraction forces around
the axes of the elements 10a and 10b generated between the permanent
magnets 3a and 3b and the opposed yokes 5a and 5b fixed on the fixation
base 9. Accordingly, under influence of the magnetic attraction forces,
the movable section 450 can be driven while maintaining a substantially
constant attitude thereof.
Moreover, if the elastic deformable elements 10a and 10b are covered with a
damping material such as silicon, the amplitude of the first-order
resonant frequency in the tangential drive characteristics can be reduced.
Extensions of the pivotal axes of the elastic deformable elements 10a and
10b both pass through the center of mass of the movable section 450 as
shown in FIG. 9A. Therefore, a dynamic balance of the movable section 450
is maintained, thereby obtaining a stable tangential drive.
When extensions of the pivotal axes of the elastic deformable elements 10a
and 10b both pass through the principal point O' of the object lens 1 as
shown in FIG. 9B, the movable section 450 pivots around O'. Therefore, the
amount of the translational movement of the object lens 1, i.e., the
movement along the circle of a disk, is reduced, thereby minimizing
time-based fluctuations of recording and reproduction signals.
Elements 13a and 13b having hinge-like shapes as shown in FIG. 10 may be
provided for supporting the movable section 450 in such a manner that the
movable section 450 pivots along the direction .+-.Tt, instead of the
elastic deformable elements 10a and 10b. In this case, the same effects
can be also obtained. Optimal spring returning forces of the hinge-like
elements 13a and 13b along the pivotal direction thereof are provided by
adjusting the material, the shape and the thickness of the hinge-like
elements 13a and 13b. If the hinge-like elements 13a and 13b and the
relaying elements 11a and 11b are combined into an integral unit, the
number of parts is decreased, thereby reducing cost.
In Example 4, for the simplification of description, an exemplary object
lens driving device is described that performs 3-axis drive including a
focusing drive, a tracking drive and a tangential drive. An object lens
driving device capable of an additional radial drive may be used where two
permanent magnets and two focusing coils are provided side by side along a
tracking drive axis like as the permanent magnets 3a and 3b and the
focusing coils 7a and 7b described above.
As described above, according to the present invention, driving means for
focusing that are deployed at the four positions and a tilt spring for
supporting fixation sections of suspension wires so that the fixation
sections can be displaced in tension and compression directions are
provided, whereby a movable section can be driven and supported in such a
manner that the movable section can readily move in four axial directions,
i.e., a focusing direction, a tracking direction, a radial tilt direction
and a tangential tilt direction.
According to the present invention, permanent magnets adhered to a movable
section and opposed yokes fixed on a fixation base produce magnetic
attraction forces which act on suspension wires in a tension direction,
whereby deformation such as buckling can be avoided, resulting in
consistently stable supporting of the movable section.
According to the present invention, a spring force of a tilt spring is
provided so as to be sufficiently greater than a tension of a suspension
wire and less than a spring force in a buckling direction of the
suspension wire, whereby precision of positioning the movable section can
be maintained while influence of buckling resonance of the suspension wire
upon the movable section is reduced.
According to the present invention, a first end of a suspension wire is
fixed to a relaying element and the relaying element is connected to a
lens holder via an elastic deformable material in such a manner that a
movable section including the lens holder can pivot, whereby it is
possible to provide an arbitrary first-order resonant frequency and
suitable drive sensitivity for a tangential drive.
According to the present invention, even when a movable section moves
toward a focusing direction, a translational movement of the movable
section in a direction of the axis of a suspension wire does not occur,
whereby the attitude of the movable section is maintained, resulting in a
stable tangential drive.
Various other modifications will be apparent to and can be readily made by
those skilled in the art without departing from the scope and spirit of
this invention. Accordingly, it is not intended that the scope of the
claims appended hereto be limited to the description as set forth herein,
but rather that the claims be broadly construed.
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